A surface acoustic wave device is electromechanical conversion device and relies on a surface acoustic wave that propagates its elastic energy concentrated at the surface of a solid. Generally, a surface acoustic wave device is provided with at least one interdigital transducer on a piezoelectric substrate. The interdigital transducer includes a pair of comb-like electrodes interdigitated with each other and each having a plurality of digit electrodes. When an electrical signal is applied on the at least one interdigital transducer of the surface acoustic wave device, the piezoelectric substrate is stressed, and this stress becomes a surface acoustic wave. Then, the surface acoustic wave propagates on the surface of the piezoelectric substrate. Operational frequency f of the surface acoustic wave device is defined by f=υ/λ, wherein υ is a propagation velocity of the surface acoustic wave and λ is a wavelength of the surface acoustic wave device which is determined by a distance across one cycle of the digit electrodes.
Nowadays, surface acoustic wave devices are widely used in wireless communication apparatuses such as mobile cellular phones, broadcasting satellites and so on. However, conventional surface acoustic wave devices generally have operational frequencies of less than 10 gigahertz. With the development of wireless communication technologies, mobile cellular phones and broadcasting satellites are likely to use higher frequencies for carrier waves. Therefore, surface acoustic wave devices can be used at a frequency band more than 10 gigahertz have been required.
What is needed is to provide a surface acoustic wave device which can be used at a higher-frequency band.